600 cc Rotax

Papee,

I don't know if you want tech stuff on this thread, or not. If not just put it where you want it.

We are bidding on a 600cc Rotax 3 cyl. engine. If we win our intentions are to use it on the Tomcat for my buddy Ron.

According to at least three sources, the engine puts out 125 HP, and weighs about 80 pounds. I know it winds up about 8000 rpms, but If geared down we are hoping it will put out plenty of push to get that Tomcat to plane out and preform good.

I don't know a lot about Rotax engines, but I figure they must not be too bad or they would not use so many in experimental aircraft.

If anyone has any advise, good or bad, I would appreciate it. ;stir;

Dave

Dave,

At 125 HP, it should make Ron's Tomcat run like its tail is on fire.

I've looked at some info on the Rotax engines, and most of what I've seen has sounded pretty good.

If I was starting over from scratch, I'd sure look into them more.

I don't really know Rotax engines, but "think" they build both air cooled and water cooled engines in that size range. I also "think" some are reduction-ready, some can be made reduction-ready, and some can not.

I also know Rotax builds both 2 cycle and 4 cycle engines, for a VERY wide range of applications.

Just make sure that you know exactly what you're bidding on.

Here's a website that may help:

http://www.rotaxservice.com/rotax_engin ... ngines.htm

And here's another:

http://www.rotax.com/en/Engine/2004/Aircraft/

Good luck with it. ;thumb;

Duane

Lets see, Half the weight and 4 times the hp of my (now deceased) Tomcat with the tired old VW engine. It went 27mph at its best. Ron's Tomcat will be scary fast ;thumb; ;thumb; ;thumb; I have rotax motors in two of my sleds and they're reliable and bulletproof. I can't wait to see it run....
Is the one you're looking at aircooled or watercooled?

Bruce

Hi Bruce,

I'm nearly positive it's watercooled. I think that's a good thing, even though, a little more work and parts to set up, also a bit more weight, Radiator, Coolant etc..

I'm just real interested to get that Tom going,, without a lot of problems up front, know what I mean?

Dave

P.S. - PM me if you want some more info.

We just found out we won the Rotax. Should be here in two or three weeks.

Now, the "fun" begins ;rasta; ;rasta;

Dave

Dave,

Woohoo ! Let the fun begin !

I'm looking forward to seeing what you do with it. I truly enjoyed the Aircat build, and I expect the Tomcat will be fun too.

I hope that you do something about the color of the head though. Maybe stealth black? ;stir;

Nah, it's already got plenty of HP. :&&:

Duane

Maybe I should be buying up all these snowmobiles up here and pulling the motors. I see at least two a week cheap.

Papee,

I have absolutely zero experience with snowmobiles. For some reason they aren't very popular in the South. :?:

I just always assumed that they all had air cooled engines. Looks like I had that wrong. :?

I know there are some of them that make some serious power, with very light engines.

It makes a lot more sense to use a snowmobile engine for a Mini, than a Turboshaft, or an antique oversize chainsaw engine. ;stir;

Thanks,

Duane

In my opinion, a snowmobile operates a lot like a boat, that is, it has to turn that stubborn track, and plow through snow. Unless you are on hardpack, it doesn't coast much when you let up on the throttle, just like a boat.

One other thing about snowmobiles, they should be easy to cool, since they usually operate in cold weather. I'm not quite sure why some of them have gone to liquid cooling. It must be because of making three little cylinders put out 125 HP, ya' think?

Dave

I've owned air cooled sleds before and what I have learned is an air temperature difference of only 20 degrees results in a noticeable change in the performance of the engine. The warmer it gets the richer the engine runs (and more sluggish) they become. The opposite is true as the temp drops. Liquid cooling makes a 2 stroke motor much more reliable. Go Dave!
However, just like a good looking woman, highly tweaked 2 stokes require more attention and are not as forgiving as a 4 stroke. However, treat them good and they'll put out just fine. Neglect them and you'll wonder what went wrong. :?: :?:
Ooops, gotta go. My highly tweaked wife needs some attention. ;stir; ;stir; ;stir;

Flathead

By the way, I got the bottom on the FATCAT today. Will post pics tommorrow.

Bruce,

I will have to stay neutral about snowmobile engines running sluggish with warmer ambient temperatures. I never noticed it. I haven't owned or ridden one since the mid 1970's. Back then they were mostly all air cooled, and it seemed to me they had all the power we needed and then some. Since then, I know they have gotten a lot faster. ;peek;

I never saw a groomed trail then either, maybe that increasesd the need for speed? :o

As far as the women goes, back in those days , no matter how I "tweaked' them, I was always wondering what went wrong. ;rasta; ;rasta; Do you mean to say I could have avoided all that by finding a water cooled model?? :&&: :&&:

Dave

Dave,

I suspect that getting that much HP out of 3 cylinders has a LOT to do with why they have gone to water cooled.

As far as higher ambient temps are concerned, I don't think it'll be a problem. One thing that water cooling does is make the engine more tolerant of different ambient temps. I've had water cooled motorcycles, and air cooled motorcycles, so I've experienced that difference.

They use a very similar engine to yours in Jet Skis, right? ;)

Duane

Duane,

I have had the same amount of experience with jet skis, as you have had with snowmobiles.

I do believe they are similar, however the cooling must be set up differently. I don't think they use a radiator.

Dave

To clarify, that's AIR cooled engines that get sluggish in warmer temps. As Duane says, water cooling makes modern 2 stroke motors much more tolerant to changes in air temperatures....

Bruce

Quote:

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Originally Posted by buster

Duane,

I have had the same amount of experience with jet skis, as you have had with snowmobiles.

I do believe they are similar, however the cooling must be set up differently. I don't think they use a radiator.

Dave

---

Dave,

I don't have a lot of personal experience with Jet Skis either, but I have been around several. I've never owned one myself, and have ridden exactly 3 of them, for maybe 30 minutes each. They are a blast to play with. I "think" that they are ALL cooled by whatever water they are in. Meaning that I "think" they have an open cooling system rather than a closed cooling system.

It's been a long time since I've played with one of them, and there was alcohol involved then, so my memory may not be correct. ;rasta;

But I've since then seen a bunch of guys warming thier Jet Skis up on the trailer, while still on the ramp, so they're ready to go as soon as they launch. Makes me wonder now...

I don't know. I DO remember opening the cowl on one, and seeing a 3 cylinder Rotax engine, with a hot pink head. :&&: :&&: :&&: I do NOT remember a heat exchanger or radiator.

Uh, that reminds me. I need to send you a NAPA part number for the stealth paint. ;stir;

Duane

i have owned over a dozen jet-skis and rebuilt most of them they r cooled by the water their in. the jet propulsion forces water into the motor. i have many of times tried to get one on my airboat the shaft is the hardest part most r splined female shafts that dont bolt together just slide in. the closest i came to mounting one on a boat was still using the jet drive and motor yamaha 550 in a 12' jon boat it was fast enough to roll u out the back of the boat on take off

Luckily the 600cc Rotax we are getting is a Bombardier from a snowmobile. It looks like it has a tapered output shaft, set up to mount a primary clutch pulley.

I suppose I'll need to find an old one someplace, as a starting point, to work out a pulley arrangement for a reduction drive, home brew of course ;stir; ;stir;

Dave

Dave,

Are you thinking of using a primary clutch as one of your pullies? I'm no expert, but I think there are ways to lock the distance between the sheaves, fixing the 'diameter' of the pulley.... The same could be done with the secondary pulley, giving you an almost infinite range of reductions to choose from. Finding a belt may be tough though..... Just thinking out loud. ;stir; ;stir; I'm looking forward to seeing this build progress ;thumb;

Bruce

Hey Bruce,

Actually what you said has crossed my mind, but without some of those parts in my hand, my thoughts are limited.

I do think you are right about the adjustment range etc., of those pulleys. Maybe, the belt length of a snowmobile will be the deciding factor for the location of the Tomcat engine.

When the engine arrives, we can start planning in earnest ;stir; ;stir;

Sure hope we get a January thaw, that would help a lot, I really hate to heat the shop when it's this cold. I'd rather spend that money on airboat gas ;thumb; ;thumb;

Dave